Direct current amplifier



Dec. 25, 1945. R. M. WILMOTTE DIRECT CURRENT AMPLIFIER Filed May 15, 1944 UN i TED STATES PATENT OFFICE 2,391,532 DIRECT CURRENT AMPLIFIER Raymond M. Wilmette, Washington, D. 0. Application May 15, 1944, Serial No. 535,764 Claims. ('Cl. 17195) This invention relates to amplifiers for direct current or slowly varying current, and means for measuring direct or slowly varying currents and voltages.

A primary object of my invention is to provide a D. C. amplifier which is substantially independent of variations of the battery voltages.

A further object of this invention is to provide an amplifier capable of amplifying either alter nating or direct current voltages without any modifications of the circuit.

Another object of this invention is {so-provide a means for measuring-direct or slowly varying currents and voltages. iv

The invention will be more fully understood from the following the drawing,

description and in which:

-- and .3. When a voltage Figure l is a schematic representation of one embodiment of my invention,

Figures 2 and 3 are diagrams illustrating the operation or the circuit in Figure l, and

Figure 4 is a modification of the invention illustrated in Figure 1.

Referring to the drawing, Figure 1 shows a pair of electron tubes Ti and T2 which may be in the same envelope, having cathodes, control grids, and anodes. A center-tapped resistor 3 is connected between the control-grids, and the secondary of an input transformer 2 and a biasing battry 3 are connected from the center tap to the cathodes. A source of alternating voltage 5 is connected across the primary of transformer 2 and impresses a voltage on both control grids in like phases, while a signal voltage E is impressed across the resistor 3. The voltage E may be a D. C. or slowly varying voltage to b amplified, but it is evident it may also be an A. C. voltage. The anodes of tubes TI and T2 are connected through a pushpull transformer 8 and a plate battery i to the cathodes. The output of tubes Ti and T2 is amplified in an A. C. amplifier l0 and cophasally impressed on the control grids of the tubes T3 and Til through a transformer l2. The A. C. voltage from source 5 is also connected through a transformer l8 to a pair of rectifiers i1 and i8. Th output of these reetifiers is impressed across resistors I3 and i4 connected .between the control grids of tubes T3 and T6 and ground. A biasing battery i5 is provided to bias tubes T3 and T4 to cutofl. The anodes of tubes T3 and T4 are connected together through a cententapped resistor 2i plate voltage, not shown, to the cathodes. The anodes may be by-passed to ground for alternating current by th condenser 22 and a meter 25 is connected directly across the anodes. It is preferred to use a zer -centered voltmeter at 25 to avoid switching a meter with a single range from one anode to the other in order to read voltages of opposite polarity.

The operation oi the circuit shown in Figure 1 be best understood by referring to Figures 2 is impressed across resistor 3 alternating voltage of the frequency of source 5 is developed in the plate circuit of tubes TI and T2 and impressed on the control grids of tubes T3 and T4 through transformer 8, amplifier l0, and transformer 12. This alternating positive half cycles of V0 drivethe grid of T4 above cutoff potential and tube 'rlcon sequently draws plate current. Hence, the voltage developed across resistor 2| will represent the magnitude and polarity of the signal voltage E. The voltage across the resistor 2| may be 25. If the meter 25 is condenser 22 may be measured 'by the meter sufficiently damped, the omitted.

Figure 4 shows a modification of the circuits of tubes TI and T2. In'this modification the'altemating voltage from source. 5 is differentially applied to the anodes of tubes Ti and T2'through a transformer 26. The cathodes of tubes TI and T2 are connected together through a potentiometer 21. The movable ta of the potentiometer is connected through a load impedance 23 to alternating voltage will appear across the load andthis will be impressed through amplifier l0 in the same manner the potentials V2 combine with remains biased below cutoil and; draws no plate current. 0n the'other handpin follower type. The advantage of the cathode follower circuit is that it has greater freedom from distortion and automatically tends to compensate for changes of the tube characteristics and other variations. The potentiometer 21 provides a means for initially balancing the circuit for a zero-reading of the voltmeter-25.

The voltage source may be a commercial 60 cycle supply or a generator developing a harmonic of 60 cycles, or a source providing any other constant frequency, which may be less than 60 cycles per second or above the audio frequency band, as well as any audio frequency. It has been found desirable in some cases to reduce the plate voltages of tubes TI and T2 to 25 or 30 volts.

The filter 29 may be incorporated in the amplifier 10. The primary purpose of the filter is to eliminate harmonics of the frequency of the voltage source 5 developed across impedance 23, and to transmit to the amplifier In only voltages of the fundamental frequency of the source 5.

One of the chief troubles experienced with D. C. amplifiers is the occurrence of errors due to the drift of battery voltages. It can be seen that the circuits I have invented are substantially free of this trouble and provide a reliable means for amplifying D. C. and slowly varying voltages ing to each half cycle of said given frequency,

means responsive to the frequency potentials and pulses for producing an amplified signal voltage and means for impressing said potentials and pulses on the last named means.

2. In combination a pushpull amplifier including a pair of electron tubes and input and output voltage output and the pulses for producing a current substantially proportional to the signal voltage means for impressing the pulses and alternating voltage output on the last named means.

5. In combination, a pair of electron tubes having control grids, cathodes andanodes, means for differentially applying a signal voltage between the control grids, a circuit from each anode to cathode including an alternating voltage source connected to the anodes differentially, a load impedance connected between said source and the cathodes across which the alternating voltage output of the electron tubes is developed, means for obtaining pulses ofnegative potential corresponding to each half cycle of the alternating voltage, means responsive to the alternating voltage output and the pulses for producing a current substantially proportional to the signal voltage. 1

6. In combination, a pair-of electron tubes having control grids, cathodes and anodes, means for differentially applying a direct currentvoltage between the control grids, a circuit from each anode to cathode, means for-deriving an alternating voltage output from the anode to cathode circuits, means for amplifying the output voltage, means for obtaining potential-pulses corresponding to each half cycle of the alternating voltage, means for combining the amplified output voltage and the pulses and producing a current substantially proportional to the signal voltage.

,7. In combination, a pair of electron tubes having control grids, cathodes and anodes, means for differentially applying a signal voltage between the control grids, means for cophasally applying an alternating voltage to the control grids, a Dushpull circuit connecting the anodes and cathodes,

circuits, means for differentially applying an input voltage to be amplified to said electron tubes, means forcophasally impressing an alternating voltage on said electron tubes, means for producing potential pulses of uniform amplitude corresponding to each half cycle of the alternating voltage, means responsive to said pulses and the alternating voltage output of the pushpull amplifier for producing a voltage substantially proportional to the input voltage.

3. In combination, a pair of electron tubes having control grids, cathodes and anodes,

having an alternating voltage output, means for obtaining pulses of negative potential corresponding to each half cycle of the alternating voltage, a second pair of electron tubes having control grids, cathodes, and anodes, means for amplifying the output voltage and impressing it in like phase on said last mentioned control grids, means for impressing the pulses on said last mentioned control grids alternately, and a pushpull output circuit connected between the anodes and cathodes of said second pair of electron tubes.

8. In combination. a pair of electron tubes having control grids, cathodes and anodes, means for differentially applying a signal voltage bemeans for differentially applying a signal voltage between the control grids, a circuit from each anode to cathode, means for deriving an alter nating voltage output from the anode to cathode circuits, means for obtaining potential pulses of uniform amplitude corresponding to each half cycle of the alternating voltage, means responsive to the alternating voltage output and the pulses for producing a current substantially proportional to the signal voltage.

4. In combination, a pair of electron tubes having control grids, cathodes and anodes, means for differentially applyinga signal voltage between the control grids, means for cophasally applying an alternating voltage to the control grids, a pushpull circuit connecting the anodes and cathodes having an alternating voltage output, means for obtaining pulses of negative potential corresponding to each'half cycle of the alternating voltage, means responsive to the alternating tween the control grids, an alternating voltage source connected to the anodes differentially, a load impedance connected between said source and the cathodes across which the alternating voltage output of the electron tubes is developed, means for obtaining pulses of negative potential corresponding to each half cycle of the alternating voltage, a second pair of electron tubes having control grids, cathodes, and anodes, means for amplifying the output voltage and impressing it in like phase on last mentioned control grids,

means for impressing the pulses on last mentioned control grids alternately, and a pushpull output circuit connected between the anodes and cathodes of the secondpair of electron tubes.

9. In combination, a pair of electron tubes having control grids, cathodes and anodes, means for differentially applying a direct current voltage between the control grids, means for cophasally applying an alternating voltage to the control grids, a pushpull circuit connecting the anodes and cathodes having an alternating voltage output, means for obtaining pulses of negative potential corresponding toeach hall cycle 01' the first men- .tiallg, a load impedance connected between said tioned alternating voltage, a second pair of elecsource and the cathodes-across which the altertron tubes having control grids, cathodes, and nating voltage output of the electron tubes is deanodes, means for amplifying the output voltage veloped, means for obtaining pulses of negative and impressing it in like phase on the last men- 5- potential corresponding to each halt cycle of the tioned control grids, means for impressing the alternating voltage, a second pair ct electron pulses on the last mentioned control grids altertubes having control grids, cathodes, and anodes.

nately, and a resistor connected in pushpuli bemeans for amplifying the output voltage and im. tween the last mentioned anodes and cathodes. pressing it in like phase on the last mentioned and a voltmeter connected across a portion or the 10 control grids. means for impressing the pulses on resistor ror measuring the polarity and magnitude the last mentioned control grids alternately, and

of the direct current voltage. a resistor connected in pushpull between the last 10. In combination, a pair or electron tubes mentioned anodes and cathodes. and a voltmeter.

having control grids, cathodes and anodes, means connected across a portion of the resistor for for differentially applying a-direct current voltmeasuring the polarity and magnitude of the age between the control grids, an alternating direct current voltage.

voltage source connected to the anodes diil'eren- RAYMOND M.

I. I f I 

